The stereochemistry of the two CH3 yields CH2 elimination steps in the biosynthesis of kaurene, the precursor to the gibberellin plant growth regulators, is to be clarified by experiments with soluble enzyme preparations using mevalonate bearing a chiral methyl group as substrate. The elucidation of the hidden stereochemistry associated with the biosynthesis of a family of biogenetically related diterpenes is proposed. The determination of the structural and biosynthetic stereochemistry of casbene, a cyclopropane-containing phytoalexin produced by enzyme extracts from castor bean seedlings, is another objective of the research. The substrate specificity of these diterpene cyclases is to be explored by use of a series of analogues of geranylgeraniol and copalyl pyrophosphates. A second major objective of the project is the elucidation of the stereochemistry attending the enzymatic oxidation of the C-19 methyl group a of kaurene through the sequences CH3 yields CH2OH yields CHO yields CO2H. These steps are involved in gibberellin biosynthesis. A combination of chemical and spectroscopic procedures will be utilized to ascertain the stereochemistry of the prochiral protons in the hydroxymethyl group. A similar investigation is proposed for studying the stereochemistry of the methyl group oxidations in sterol biosynthesis.